Def. Tech Studio Monitor 65's with a CS-8080 center

That setup would work just fine as all of the newer Definitive Technology are voiced the same, in order for them to all work together. The third SM-65 would likely have more oomph than the CS-8080 due to the SM-65 having larger drivers. That would be the best way to go. No matter which speaker brand you go with, having a 3rd matching speaker to the Lefts and Rights is always the best and most preferable way to do it as the horizontal placed center channels are always a design compromise only made that way in order to be more space effecient.

Hello Ten, personally I would suggest a CS-8080 center, if you can swing it. The powered sub in the middle can really help with dialog and effects realism. The SM 65 is also a fine choice if you can't gather up the bucks for the CS-8080, but as you say that your main usage is movies, you really want the dialog to be as realistic as possible. No worries about timbre-matching issues from our perspective. I hope this helps - best, Joe

You can get the sm350/450 for around 200 dollars/ pr from New Egg!